The invention relates to the domain of sealing metal caps, and more particularly to sealing metal caps with threaded plastic inserts adapted to glass screw tops. These caps are designed particularly for closing receptacles, flasks and bottles containing alcohol and spirit.
Sealing caps with plastic inserts, typically SUPALUXE(copyright) caps marketed by the applicant, consist of a metal cap, a plastic insert, and possibly a seal if the insert itself does not perform the sealing function.
The plastic insert is assembled inside the metal cap by force fitting the insert into the metal cap.
FIG. 2 shows a typical cap according to the state-of-the-art with an add-on seal. As can be seen in the figure, the major advantage of this type of cap is that the outer metal cap itself is not threaded, which improves the esthetic quality of the cap and packaging, typically a flask or a bottle. Furthermore, the threaded plastic insert can be used for a large number of closing/opening cycles, therefore screwing/unscrewing cycles, without changing the geometry of the cap, which is an essential requirement for receptacles containing alcohols and spirits.
The problem that arises with these caps is essentially related to unscrewing the cap, particularly when the contents of the receptacle contain sugar or any other product that could crystallize. Crystallization of the sugar contained in the liquid in the bottle can prevent the plastic insert from sliding around the glass top, such that when an attempt is made to unscrew the cap, the metal cap slides on the insert, since cohesion between the glass top and the insert is greater than cohesion between the metal cap and the insert, which makes it impossible to open the bottle.
An attempt was made to solve this problem by increasing the limiting torque at which the metal cap and the insert separate in rotation. The applicant attempted to do this by reducing the tightening clearance between the insert and the metal cap, increasing the roughness of surfaces in contact, modifying the nature of the insert, and adding an adhesive or hot-melt coat between the metal cap and the insert. These measures do not solve the problem that arises.
According to the invention, the sealing cap with a plastic insert for closing screw top receptacles comprises a metal cap composed of a head and a skirt, a plastic insert, placed inside the said metal cap and rigidly fixed to it by an attachment means, and is characterized in that the said attachment means consist of a coat bonded to the said metal cap extending over all or part of the said metal cap facing the said insert, in that the said coat comprises the said plastic material in the divided state, and that it is heat sealed to the said insert.
Preferably, the said coat extends over the entire surface of the said metal cap facing the said insert.
If the said coat covers the entire inside surface of the said metal cap, problems can arise when closing the bottle due to the fact that the final cap is unable to slide.
The solution found by the applicant considerably increases the sliding torque of the insert inside the metal cap, typically multiplying it by a factor of 6. This torque measured according to standard NF H 35103 is increased from 17 lbs.inch (1.9 N.m) to more than 100 lbs.inch (11.3 N.m).
The means according to the invention provide a complete solution to the problem that arises. No separation was ever observed between the insert and the metal cap with any of the caps made according to the invention, even with very crystallized sugar deposits.